Wire electric discharge machining method

ABSTRACT

A wire electric discharge machining method capable of performing a first machining and also a second cut-off machining based on a single machining program. A program for defining machining paths for cutting off individual male forms A1-A3 is inputted and a reserve amount α and a backward amount β are set. In the first machining, the electric discharge machining is stopped with the reserve amount α left, and this stop position is stored. In the second cutting machining, an automatic wire connection is performed at a wire connecting position turned back by the backward amount β from the stop position along the machined groove which is formed in the first machining, and then the male forms A are successively cut off by performing the discharge machining from the wire connecting position. A wire discharge machine has an annealing/fusing device for annealing and fusing the wire with heat generated by an electric current flow in the wire. Since the wire is made straight by the annealing and a cut end thereof is made hemispheric, the wire can be easily inserted into the machined groove.

TECHNICAL FIELD

The present invention relates to a wire electric discharge machiningmethod, and more particularly to a wire electric discharge machiningmethod for cutting male forms off a workpiece.

BACKGROUND ART

In a wire electric discharge machining, if the machining is completed onall the commanded machining path, a male form drops to possibly collidewith a lower wire guide and damage it. Especially in machining aplurality of forms from a single workpiece, when the machining of oneform is completed, it is necessary to cut a wire electrode and move theworkpiece to be positioned at a machining start hole for the nextmachining form, and to automatically connect the wire electrode throughthe next machining start hole. The dropped male form might slide on thelower wire guide in moving the workpiece to cause damage to the lowerwire guide. Therefore, a first machining is performed on a great part ofthe machining form and is stopped immediately before the male formdrops, to proceed to the next machining form with the male formremaining on it. Then, the electric discharge machining is performed onthe next machining path to a position immediately before the male fromdrops. In a second machining, each male form is cut off the workpiece inthe presence of an operator.

The following two methods are known for performing the second machining.

(1) The wire electrode is inserted through the machining start hole andis moved along the already machined groove with the electric dischargeoff (or with the electric discharge on), thereby cutting off thereserved section by the electric discharge machining. This method isadopted for a male form of relatively light weight. (2) After clampingthe male and female forms so as to be bridged therebetween on the firstmachining path to hold the male form, the wire electrode is insertedthrough the machining start hole and then the workpiece is movedreversely in the second machining path to perform the electric dischargemachining, thereby cutting off the reserved section.

In the method (1) of the above two methods, when the wire electrode ismoved along the machined groove with the electric discharge off, thewire electrode might be stuck as it is caught by the workpiece. When thewire electrode is moved along the machined groove with the electricdischarge on, the male form might be deformed as the electric dischargemachining is performed twice. In the method (2), it is necessary tocreate a machining program to move the workpiece reversely. In either ofthe two methods (1) and (2), it is required to prepare two machiningprograms for the first machining and the second cutting-off machining.

Thus, in the foregoing conventional wire electric discharge machiningmethods, two programs are necessary for the first machining to leave areserve section and the second machining to cut off a male form bymachining the reserve section.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a dischargemachining method capable of performing both first machining and second(cutting-off) machining based only on a single machining program.

A wire electric discharge machining method of the present invention isperformed using a wire electric discharge machine having anannealing/fusing device for annealing a wire into a straight shapeupstream of an upper wire guide in a wire path and fusing the wire nearthe upper wire guide, and an automatic wire connecting device forautomatically connecting the wire by restricting the wire by a machiningfluid flow from a nozzle of the upper guide.

A machining program defining a plurality of machining paths eachcorresponding to each male form is inputted, and a cutting reserveamount and a backward amount for a second discharge machining is set. Ina first discharge machining, the wire is automatically connected througha machining-start hole in the first machining path by the automatic wireconnecting device, to perform an electric discharge machining forshaping along the first machining path based on said machining program,the electric discharge machining is stopped at a stop position with saidreserve amount left along the first machining path to anneal and fusethe wire by the annealing/fusing device, and performing and stopping theelectric discharge machining along successive machining paths.

In the second discharge machining, the wire is automatically connectedat a wire connecting position turned back by said backward amount fromsaid stop position along a machined groove formed in the first electricdischarge machining, the electric discharge machining is performed fromthe wire connecting position along the first machining path based on themachining program to cut off a first male form, the wire is annealed andfused by the annealing/fusing device, and the male forms aresuccessively cut off.

The annealing/fusing device anneals the wire by flowing an electriccurrent in the wire through two wire fusing electrodes disposed on astraight line with a predetermined distance therebetween in the wirepath upstream of said upper wire guide, and fuses the wire in thevicinity of one of said wire fusing electrodes, which is disposed nearthe upper wire guide.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a principal part of a wire electricdischarge machine for carrying out a wire electric discharge machiningmethod of the present invention;

FIG. 2 is a functional block diagram of a controller of the wireelectric discharge machine as shown in FIG. 1;

FIG. 3 is a flowchart showing the process of cutting off male formsaccording to one embodiment of the invention; and

FIGS. 4(a), 4(b) and 4(c) are schematic views of an example machiningaccording to the electric discharge machining method of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

First, a general structure of a wire electric discharge machine forcarrying out the electric discharge machining method of the inventionwill be described, referring to FIG. 1. FIG. 1 shows a principal part ofa wire electric discharge machine for carrying out the method of theinvention. In FIG. 1, the whole body of the wire discharge machine isgenerally divided into two sections of oppositely arranged upper andlower machine frame sections 1 and 2, which are attached to anon-illustrated column so that they are vertically movable with respectto each other. The upper and lower machine sections 1 and 2 are arrangedso as to adjust a distance between the upper guide 7 upstream in a wirefeeding path and lower guide 8 downstream in the wire feeding path inaccordance with a thickness of a workpiece to be machined.

A wire winding unit 3, a brake roller 4, a wire fusing mechanism 5, awire lead-in unit 6 and the upper guide 7 are disposed on the uppermachine section 1.

The wire winding unit 3 comprises a supply reel 9 operatively connectedto a winding motor 8, and the brake roller 4 is driven by a reversiblebraking motor 1 via a timing belt, a powder clutch, etc. A pulse coder 1detects the amount of rotation of the brake roller 4 (the amount ofmovement of the wire).

The wire fusing mechanism 5 is composed of a wire feed pipe structure 12disposed upwardly of the upper guide 7, first and second wire fusingelectrodes 13 and 14b disposed at inlet and outlet sides, respectively,of the pipe structure 12, and a pressure roller 15. The second wirefusing electrode 14b serves as a substantial wire fusing means and alsoas a wire-end detector as 14a.

The electrode 14b and the pressure roller 15 are movable toward and awayfrom a wire path. Specifically, the electrode 14b and the pressureroller 15 are moved so as to enter a path of the wire 20 by anon-illustrated solenoid with a controlled current-supply when theelectrode 14b is used as the wire fusing means or the wire-end detectingmeans, and they are moved away from the wire 20 in the electricdischarge machining. The wire 20 is annealed and fused by supplying anelectric current to the wire 20 via the first and second wire fusingelectrodes 13 and 14b while flowing a cooling air between points A and Bin the wire feed pipe structure 12. The wire 20 is heated by thiselectric current to be annealed. As the cooling air does not flow in thevicinity of the wire fusing electrodes 14b, the temperature of the wire20 rises sharply in this region, as compared with a region where thecooling air flows, to fuse the wire 20.

An upper electrode 30a for machining is arranged to face the wire pathin the upper guide 7 and in the electric discharge machining an electriccurrent is supplied between the upper electrode 30a and a lowerelectrode 30b for machining.

In the lower machine section 2, a wire drawing roller 17, a pinch roller16 confronting the wire drawing roller 17, and the lower guide 18 arearranged. Reference numeral 19 designates a table surface of the wiredischarge machine. The lower electrode 30b for machining is disposed toface the wire path in the lower guide 18. Reference numerals 31a and 31bdesignate inlets from which a machining fluid is introduced and theintroduced machining fluid is spouted towards the machining area fromnozzles of the upper and lower guides 7 and 18.

The wire 20 drawn from the supply reel 9 is guided by deflector rollers21, 22 to the brake roller 4, and then passes the first wire fusingelectrode 13 to reach the upper guide 7 through the wire feed pipestructure 12, whereupon the wire 20 passes the lower guide 18 and isguided by the deflector roller 23 to reach the wire drawing roller 17,to thus define the wire path. The wire 20 runs along the wire path bythe pulling action of the wire drawing roller 17 under a predeterminedbackward tension given by the brake roller 4, which is driven by thebraking motor 10 under control of a constant current circuit. The lowermachining electrode 30b in the lower guide 18 as well as the uppermachining electrode 30a come into contact with the running wire 20 tosupply an electric power for machining to the wire 20.

While the wire 20 is normally running (in the electric dischargemachining), the winding motor 8 of the supply reel 9 rotates idly in adirection (indicated by a dotted-line arrow) opposite to the winding-updirection. At that time, the gripper 26 assumes an open posture out ofcontact with the wire 20.

Reference numeral 24 designates a pinch roller abutting acircumferential surface of the brake roller 4 to ensure the contactbetween the wire 20 and the brake roller 4. In the lower machine section2, the wire 20 is inserted into a guide pipe 25 disposed between thedeflector roller 23 and the wire drawing roller 17.

The wire lead-in unit 6 is composed of an arm 27 having a clamp 26 atthe distal end thereof and an air cylinder 28 for retracting the arm 27,the clamp 26 being disposed downstream of the pressure roller 15. Thewire pulling unit 6 serves as a means for removing the wire.

The wire feed pipe structure 12 has non-illustrated intake and exhaustports at the respective positions indicated by arrows A and B. As ispreviously described, the wire 20 is annealed between the two positionsA and B and fused at the position of the second wire fusing electrode14b. The wire feed pipe structure 12 is entirely electrically insulatedfrom the wire 20.

Further, the wire feed pipe structure 12 is supported by a slide member102 together with the first fusing electrode 13, and the slide member102 is driven upwardly and downwardly (through a length L) along a postguide 103 between the illustrated uppermost position and a lowermostposition defined by the a positioning portion 71 on the upper guide 7 bya non-illustrated driving means. This pipe structure 12 is used for theautomatic wire connection.

In FIG. 2, a reference numeral 50 designates a control system for a wireelectric discharge machine, which also serves as a numerical controlsystem for controlling the position of the table 19. The control system50 includes a central processing unit (CPU) 51 in the form of amicroprocessor, to which a program memory 52, a data memory 53, anoperation panel 54 with a liquid crystal display LCD, and aninput-output circuit 55 are connected via a bus 56.

The program memory 52 stores various programs for controlling individualparts of the wire discharge machine and the control system itself Thedata memory 53 stores a machining program and various setting data fordetermining machining conditions and also used for temporary storage ofdata in various calculations by the CPU 51.

To the input-output circuit 55, a table drive section 60, a machiningpower source section 61, a wire fusing power source section 62, a wirewinding/drawing control section 63, a wire feed control section 64, thepulse coder 11, an electrode-function switching section 66, a tapereader 67, a wire-end detecting section 68, a CRT display device, and amotion control section 70 for controlling individual parts of the wireelectric discharge machine are individually connected.

The table drive section 60 and the machining power source section 61 areof a well known constitution and controlled according to the ordinarymethod in executing the electric discharge machining. The wire fusingpower source section 62 supplies necessary electric power to the firstand second wire fusing electrodes 13 and 14b. The wire winding/drawingcontrol section 63 controls a motor (not shown) for driving the wiredrawing roller 16 and the winding motor 8.

Further, the wire feed control section 64 controls the motor 10 fordriving the brake roller 4, and the amount of rotation of the brakeroller 4 is detected by the pulse coder 11, as previously mentioned.

The electrode-function switching section 66 selectively switches thefunction of the second wire-fusing electrode between the secondwire-fusing means as 14b and the wire-end detecting means as 14a, and awire-end detection signal from the electrode 14b as the wire-enddetecting means is inputted to the wire-end detector 68.

The motion control section 70 for various parts controls the back andforth motions of the second wire-fusing electrode 14b and the upward anddownward motions of the pipe structure 12, etc.

The method of the present invention is carried out using the wireelectric discharge machine having the above-described wireannealing/fusing function and automatic wire connecting function. Forcutting the connected wire electrode, an annealing/fusing process isperformed according to the following procedure. After stopping themachining and invalidating all the machining conditions, the driving ofthe wire drawing roller 17 and the brake roller 4 is stopped. Then,cooling air is supplied into the pipe structure 12 via the intake portand the wire 20 is gripped by the gripper 26. While pulling the wire 20in the winding direction by driving the winding motor 8, an electriccurrent is supplied to the wire 20 between the wire fusing electrodes 13and 14b through these electrodes 13 and 14b to heat and anneal the wire20 . At that time, the temperature of the wire 20 rises sharply at theposition of the second wire-fusing electrode 14b where no cooling airflows and, as a result, the wire 20 is fused at that position. When thewire 20 is fused, the pulling of the wire 20 by the winding motor 8 isstopped and the gripping of the wire 20 by the gripper 26 is released,whereupon the lower side of the fused wire is collected into a wirecollecting box by driving the wire drawing roller 17. Then, the brakeroller 4 is driven to feed the upper side of the fused wire until a cutend thereof is detected by the wire-end detector 14a, to terminate thewire cutting process. Curls of the upper-side wire between the first andsecond wire-fusing electrodes 13 and 14b is eliminated by the annealingto thereby make the wire straight, and at the same time the cut end ofthe upper-side wire is shaped into a hemisphere having a smooth surfaceby the fusing.

In an automatic wire connecting process, while feeding the wire 20 bydriving the brake roller 4 by the braking motor 10, the wire feed pipestructure 12 is lowered to be engaged with the positioning portion 71.Then, the machining fluid is supplied to the wire feed pipe structure 12and the guide pipe 25 to flow there in the wire-running direction, andat the same time the machining fluid is spouted from the nozzle of theupper guide 7 to facilitate feeding of the wire 20 by the brake roller4. Since a leading end of the wire 20 has the hemisphere shape with thesmooth surface by the fusing, and the wire 20 is made straight by theannealing, the wire 20 restricted by the machining fluid is insertedinto the machined groove smoothly. When it is detected (by anon-illustrated detector) that the wire 20 has passed the wire drawingroller 17 and the pinch roller 16 as guided by the machining fluidflowing in the guide pipe 25, the automatic wire connecting process isterminated. The annealing/fusing process and automatic wire connectingprocess are described in detail in International ApplicationPCT/JP96/01245 and International Laid-Open Publication WO95/02482, forexample.

FIGS. 4(a), 4(b) and 4(c) show an example of machining in which threemale forms are cut off a single workpiece according the electricdischarge machining method of the invention. In the machining program, afirst machining path from a machining-start hole H1 through intermediatepositions P1-1, P1-2, P1-3, P1-4, P1-5 to the final position P1-1 forcutting off a male form A1, a second machining path from amachining-start hole H2 through intermediate positions P2-1, P2-2, . . ., P2-9 to the final position P2-1 for cutting off a male form A2, and athird machining path from a machining-start hole H3 through intermediatepositions P3-1, P3-2, . . . , P3-13 to the final position P3-1 forcutting off a male form A3 are programmed, and the machining program isinputted in the data memory 53 via the tape reader 67. Further, acutting reserve amount α and a backward amount β for a second(cutting-off) machining are set and stored in the data memory 53 fromthe operation panel 54.

When a first machining command is inputted, the processor 51 performsthe above-described automatic wire connecting process at themachining-start hole Hi in the first machining path. Then, the processor51 performs the electric discharge machining along the programmedmachining path from the machining-start hole H1 to the position P1-5 andcontinues the machining on the final block (from the position P1-5 tothe position P1-1) to stop the machining at the position P1-6 where aleft amount of the motion reaches the set reserve amount α (Since theprocessor 51 reads the machining program one block ahead, it cananticipate the final machining block for cutting off the male form A1).The processor 51 stores data representing the position P1-6 in the datamemory 53. Subsequently, the processor 51 performs the above-describedwire annealing/fusing process, and moves the workpiece to themachining-start hole H2 of the second machining path to perform theautomatic wire connecting process at the machining-start hole H2,whereupon the processor 51 performs the electric discharge machiningalong the machining path from the machining-start hole 2 to the positionP2-9. When a left amount of the motion from the position P2-9 reachesthe set reserve amount α, the processor 51 stops the machining andstores data representing the position P2-10 in the data memory 53, thenperforms the wire annealing/fusing process, and then moves the workpieceat the position of the machining-start hole H3 of the third machiningpath. The processor 51 performs the automatic wire connection at theposition of the machining start hole H3, then performs the electricdischarge machining from the machining-start hole H3 to the positionP3-13 along the programmed machining path. The processor continues themachining to the position P3-14 where a left amount of the motionreaches the cutting reserve amount α, whereupon the processor 51 storesdata representing the position P3-14 in the data memory 53 and performsthe wire annealing/fusing process, thus completing the first machining.

Upon completion of the first machining, an operator clamps theindividual male forms and the female form to be bridged on the groovemachined in the first machining so as to hold them and inputs a secondmachining command.

When the second machining command is inputted, the processor 51 startsthe male-form cutting-off process shown in the flowchart of FIG. 3.First, the processor 51 sets the index i to "1" (Step S1), then reads aposition stored in the i-th address (the first position is P1-6 in theexample of FIG. 4) of the data memory 53 which stores the machining-stoppositions, and then positions the workpiece so that the wire pathbetween axes of the upper guide 7 and the lower guide 18 is aligned withthe read position (Step S2). The processor 51 reads the machiningprogram for the i-th machining form, and then performs a reverse processto move the workpiece backwardly by the set backward amount β from theread position along the machining path of the machining program so thatthe wire path is aligned with the position upstream of the position P1-6by the set backward amount β (Steps S3, S4). The above-describedautomatic wire connecting process takes place at this position. The wireis automatically connected through the machined groove formed in thefirst machining (Step S5). As the wire 20 has been fused, a leading endthereof has a hemisphere shape with a smooth outer surface, and as thewire 20 has been annealed by heating it is made straight. Further, sincethe position at which the automatic wire connection is performed is setby turning back the machined groove by the backward amount β from themachining-stop position, spaces are formed horizontally symmetricallywith respect to the wire when inserting the wire into the groove definedby two cut surfaces, so that possible disturbance of the machining fluidspouted in the automatic wire connecting is reduced. Accordingly, thewire is easily inserted through the machined groove as restricted by themachining fluid at the wire connecting position.

After the automatic wire connecting process has been completed, theprocessor 51 turns off the reverse process and then restart the electricdischarge machining from the wire connecting position to perform themachining according to the machining program to the end point of themachining shape, to cut off the male form (Step S7, S8). If the index iis "1", the processor 51 performs the electric discharge machining fromthe position P1-6 to the position P1-1 to cut off the male form A1.

Further, the processor 51 performs the above-described wireannealing/fusing process and increase the index i by "1" (Steps S9, S10)and then discriminates whether or not the machining stop position isstored in the i-th address of the data memory (Step S11). If it isstored, the processor 51 reads the machining stop position and thenreturns to the Step S2 to repeat the foregoing processes.

Namely, if the index i is "2", in the example of FIG. 4, the processorperforms the automatic wire connecting process at the position turnedback by the backward amount β along the machining path for the male formA2 from the position P2-10, and then performs the electric dischargemachining from the wire connecting position by the reserve amount α, tothereby cut off the male form A2. Likewise, the processor 51 performsthe automatic wire connecting process at the position turned back by thebackward amount β from the position P1-14 in the machining path for themale form A2, and then performs the electric discharge machining by thereserve amount α, thus completing the second machining.

As described above, according to the present invention, the firstmachining and also the second machining for cutting off the male formcan be performed based on a single machining program by setting thereserve amount and the backward amount. It is therefore not necessary tocreate first and second machining programs individually which arerequired in the prior art. Further, as the automatic connecting processis performed at the position turned back by the backward amount alongthe machining path from the position where the machining is reserved bythe reserve amount and the discharge machining is started at thatposition in the second machining, the second machining is performedspeedily to thereby reduce the machining time.

We claim:
 1. A wire electric discharge machining method for cutting aplurality of male forms off a workpiece using a wire electric dischargemachine having an annealing/fusing device for annealing a wire into astraight shape upstream of an upper wire guide in a wire path and fusingthe wire near the upper wire guide, and an automatic wire connectingdevice for automatically connecting the wire by restricting the wire bya machining fluid flow from a nozzle of the upper guide, said methodcomprising the steps of:(a) inputting a machining program defining aplurality of machining paths corresponding to the respective male formsand setting a reserve amount for a first electric discharge machiningand a backward amount for a second discharge machining; (b) performingthe first discharge machining by (b1) automatically connecting the wirethrough a machining-start hole in the first machining path by saidautomatic wire connecting device, to perform an electric dischargemachining for shaping along the first machining path based on saidmachining program, (b2) stopping the electric discharge machining at astop position with said reserve amount left along the first machiningpath, to anneal and fuse the wire by said annealing/fusing device, and(b3) performing and stopping the electric discharge machining alongsuccessive machining paths in the same manner as said steps (b1) and(b2); and (c) performing the second discharge machining by (c1)automatically connecting the wire at a wire connecting position turnedback by said backward amount from said stop position in said step (b2)along a machined groove formed in the electric discharge machining ofsaid step (b1), (c2) cutting off a first male form by performing theelectric discharge machining from said wire connecting position alongthe first machining path based on said machining program, (c3) annealingand fusing the wire by said the annealing/fusing device, and (c4)cutting off said plurality of male forms successively in the same manneras said steps (c1), (c2) and (c3).
 2. A wire electric dischargemachining method according to claim 1, wherein said annealing of thewire by said annealing/fusing device is performed by flowing an electriccurrent in the wire through two wire fusing electrodes disposed on astraight line with a predetermined distance therebetween in the wirepath upstream of said upper wire guide, and said fusing of the wire isperformed in the vicinity of one of said wire fusing electrodes, whichis disposed near the upper wire guide.